The present invention relates to a process for refining gold comprising dissolving unrefined gold of relatively low purity into a solution and precipitating the gold by use of an alkali to obtain the the gold of high purity. The invention further relates to an apparatus which effectively carries out gold refining without adding any reagent by, after dissolving gold of relatively low purity into a solution, obtaining gold of high purity by means of precipitation employing an alkali, and by circulating the solution used for the refining, and to a process for refining gold employing the apparatus.
Heretofore, the following processes and the like have been known as gold refining processes; a process which comprises dissolving low grade gold by aqua regia or hydrochloric acid-chlorine solution and selectively reducing only gold by such a reducing agent as hydrazine; a process which comprises refining low grade gold in the acidic environment of hydrochloric acid by electrolysis.
However, the former process requires the equipment and labor for disposal of waste gases, and the latter process has the drawback that it generates chlorine gas at the anode since hydrochloric acid is employed as an electrolyte so that its electrolysis efficiency is low.
Also in the latter process, the concentration of the gold should always be maintained high, and in order to generate no chlorine gas, electrolysis should be carried out at a lower current density of not more than 3 A/dm.sup.2 and consequently production capacity is low and excessive facilities are required.
As an improvement of a process for recovery of gold, a process has been known which comprises dissolving a gold compound as potassium gold iodide employing iodine and an iodide compound, and reducing the gold compound by means of a reducing agent to deposit and recover the gold (U.S. Pat. No. 3,957,505). Since the process is not a process for refining gold but a process for recovery of gold, no special consideration is given to the removal of impurities in the potassium gold iodide dissolved by use of iodine and the like though the existence of the impurities themselves may be recognized.
In the process of refining gold, it is required to effectively utilize reagents employed in the refining system to enhance the operation efficiency. In the prior art including the above U.S. patent, no or slight consideration is given to the enhancement of the operation efficiency, and the grade of gold obtained and its purity